Oil mist separators (OMS) are used in engines to separate oil and soot from blow-by gases coming from the crankcase. The unclean blow-by gases enter through the top of the OMS, which functions as a centrifuge to separate the oil from the air or gas, thus cleaning the air or gas. The OMS contains disc stacks, which consists of closely spaced conical discs that spin. The disc stacks are rotated by a turbine on the bottom of the OMS that is driven by oil from the oil gallery. Blow-by gases are forced through the gaps of the rotating discs.
Oil droplets, soot, and aqueous acidic combustion condensate settle onto the upper surface of the lower cone due to the high centrifugal acceleration in each gap. The disc sacks spin the liquid film to the outer annulus until the liquid is spun off the disc stack and onto the outer housing. The liquid drains down the wall to the oil sump and the clean blow-by gas travels up the outer annulus and out of the clean blow-by exit. Additional oil travels up the inside of the rotating shaft to lubricate the bearing at the top of the oil mist separator. The oil wetting the bearing then drains back into the oil mist separator where it is separated from the blow-by gas and drained back into the oil sump. The OMS may become clogged, for example with soot and/or sludge, from engine oil exhaust. Keeping the OMS clean may be key to preventing clogging and preventing failure of drainage channel in engines such as heavy duty diesel engines.
Many different chemicals may contribute to the formation of and levels of soot or sludge in an engine crankcase and OMS. New additive compositions and lubricating oil compositions capable of controlling soot concentrations and sludge build up.